The right electric fireplace size depends on two things, the width of the wall you are filling and the amount of heat your room needs.
Here is a simple way to get both right, with a few good examples to help you picture it.
Start With Your Wall Width, Not Your Room Size
The easiest way to size an electric fireplace is to start with the wall, because the fireplace is the piece everyone looks at, and it needs to look balanced there.
A good rule of thumb is that the fireplace should cover roughly half to two-thirds of the width of the wall it sits on, so a 12-foot wall suits a unit of about 50 to 70 inches.
Some designers prefer a slightly smaller fireplace, closer to one-third or one-half of the wall, so it is worth sketching the options before you decide.
It also helps to know the common sizes, since most wall-mounted units run from about 50 to 74 inches wide, TV stands with fireplaces are usually 58 to 70 inches wide and freestanding mantels are often 40 to 55 inches wide.
Bestier 70-Inch Fireplace TV Stand
The Bestier 70-Inch Fireplace TV Stand is a good example of a matched set, because it is 70.87 inches wide, supports TVs up to 75 inches and has a 23-inch insert rated at about 5,120 BTU.
Check its current price on Amazon
How Much Heat Does Your Room Need?
Most electric fireplaces run on a standard 1,500-watt outlet, which produces about 5,100 BTU of heat, and that is usually enough to warm a room of about 400 to 500 square feet.
Infrared quartz stoves are often rated for larger spaces, up to about 1,000 square feet, which makes them a better fit for big or open rooms.
A simple rule of thumb is about 10 watts of heat per square foot if you want the fireplace to do the heavy lifting, though your climate and your insulation make a big difference.
Sizing a Fireplace Under a TV
If you plan to put a TV above or beside the fireplace, the fireplace usually looks best when it is about the same width as the TV or a bit wider.
A handy shortcut is to multiply the TV width by 1.0 to 1.3 to find a comfortable fireplace width, so a 65-inch TV that is about 57 inches wide pairs well with a fireplace of roughly 57 to 74 inches.
If you would rather combine the two, a fireplace TV stand does the sizing for you.
Sizing for a Big or Open Room
When the room is large, the heat rating often matters more than the width of the unit, because one small fireplace will only warm the area around it.
In that case, look for a model rated for 1,000 square feet or more, and plan to use it as a zone heater for the seating area rather than the whole space.
Duraflame 3D Infrared Quartz Fireplace Stove
The Duraflame 3D Infrared Quartz Fireplace Stove is only 24 inches wide, yet it is rated at 5,200 BTU for rooms of up to 1,000 square feet, which shows how little the width has to do with the heating power.
Check its current price on Amazon
Sizing for a Small Room or Bedroom
In a bedroom or a small living room, a smaller fireplace is usually the better choice, because a huge unit can overwhelm the room and add more heat than you need.
Freestanding mantels of about 40 to 45 inches wide, or compact stoves, tend to look natural in these spaces and are easy to place near an outlet.
A dimmable flame and an adjustable thermostat also help, since a small room warms up quickly.
Leave Room Around the Fireplace
Whatever size you choose, give the fireplace some breathing room, with a few feet of clear space in front and a little extra on each side.
Keep curtains, rugs and furniture away from the front of the unit, and make sure an outlet is close, because extension cords are not recommended for heaters.
If you are installing a recessed unit, check the wall depth and the stud spacing before you buy, because the frame needs to fit exactly.
Heat output does not grow with the width of the fireplace, so a long unit and a compact one often produce the same warmth.
Corner rooms are a special case, and a corner TV stand with a built-in fireplace can make an awkward space feel finished.
If you are not sure, measure the wall twice and sketch the fireplace on paper first, because it is much easier to change a drawing than a purchase.
FAQ
What size electric fireplace do I need for a 12 by 15 foot room?
That room is about 180 square feet, so a standard 1,500-watt fireplace has plenty of heating power, and the width should be chosen to suit the wall.
Is a bigger electric fireplace always better?
Not for heat, because a wider unit usually produces the same warmth as a smaller one, but a bigger one can look better on a large wall.
What size electric fireplace fits under a 65-inch TV?
A TV that size is about 57 inches wide, so a fireplace of roughly 57 to 74 inches usually looks balanced beneath it.
How much space do I need around an electric fireplace?
A few feet of clear space in front and some room on each side is a safe general guide, but always follow the manual.
Conclusion
Choosing the right electric fireplace size comes down to the wall you have, the TV you own and the warmth you want.
Once you have those three numbers, picking a model is easy, and you can choose with confidence.
If you are also thinking about warmth for the rest of the house, you might like our guide to the best WiFi controlled space heaters.